A gas generator which will rapidly inflate and deploy an airbag for protecting a passenger from an impact during a collision of the automobile is installed into an airbag module which is mounted into a steering wheel or an instrument panel. Then, the gas generator allows a squib to ignite through energization of a control unit (actuator) to burn the gas generants by the ignition flame, thereby generating a great amount of gas abruptly.
In conventional gas generators, there are available a two-cylinder type gas generator which is provided with a central space corresponding to an ignition chamber of gas generants and an annular space corresponding to a combustion/filter chamber which is concentrically formed at the external part and in which gas is burnt and cooled or slag is collected. This type of gas generator includes that disclosed in Japanese Published Unexamined Patent Application No. 9-207705 which is shown as an example in FIG. 4. This drawing shows an approximate half of the radial cross section of a short cylindrical gas generator. In this gas generator, a housing structure obtained by placing a two-cylinder-structured upper vessel 51 with a double short-tube-structured lower vessel 54 and subjecting them to friction welding (housing for the gas generator) is used as an ignition chamber P at the central space and used as a combustion chamber G and a filter chamber P at the annular space in the periphery.
A squib 68 and an enhancer 69 are incorporated inside the ignition chamber P from below. Meanwhile, a concaved ring-shaped lid member 66 having a double flange on the cross section is fixed in the combustion chamber G and the filter chamber F by allowing each flange of 66d and 66e to respectively contact with burrs 52b and 53b of an upper vessel 51, and gas generants 57 and a cooling/slag-collecting member 60 are housed radially in sequence into an annular space sandwiched between the lid member 66 and the upper vessel 51, thereby forming the combustion chamber G and the filter chamber F.
Further, ring-shaped cushion members 58 and 59 are set respectively on an upper face 70 and a lower face 71 of the layer of the gas generants 57. In addition, seal members 61 and 62 are respectively set on the upper face and the lower face of the cooling/slag-collecting member 60. Moreover, an aluminum foil member 64 for closing a gas discharging orifice 53a and an aluminum foil member 65 for closing a burning orifice 52a are attached. The above-described constitution makes it possible to provide a gas generator which can sufficiently withstand a rise in inner pressure due to gas generated inside the gas generation chamber G.
However, as shown in FIG. 4, this kind of two-cylinder type gas generator is larger in the number of parts for constituting the gas generator and is complicated in structure. Therefore, some limitations are imposed on reducing the manufacturing cost thereof, while maintaining the safety of the gas generator.